Protective mask (1) comprising a frame (5) for mounting on a user's face, a window (2) carried by said frame, an optical display system (10) which is capable of projecting an image, and a prism (20) capable of receiving said image from said display and forwarding it, characterised in that the prism (20) has a first (21) and a second (22) active face and a basal face (23), the window having, on its inner face (3), a projection area (30), and said display and said prism are configured so that said display projects said image onto the first active face (21), the image crosses the prism and is reflected by the basal face (23) to the second active face (22), the image is projected from said second active face (22) onto said reflection area (30) of said window (2), and said window projects said image into a user's eye.